Ink jet type printers employ a printing head that consists of a series of nozzles, or orifices positioned in an orifice plate for expelling ink onto a printing surface. The ink can be expelled by a variety of means, including continuous, piezoelectric, and thermal/bubble jet. While several different ink jet technologies have evolved over the past two decades, the most popular ink jet technology today is the bubble jet where ink within a chamber is locally superheated to form an expanding bubble which propels a drop of ink through an orifice and onto the printing surface. Piezoelectric printers function in a similar manner inasmuch as ink is expelled through an orifice. However, instead of boiling the ink in a chamber, the ink is essentially squeezed from the chamber as a result of deflections/expansions generated by a piezoelectric ceramic transducer. The ceramic transducer changes its physical dimensions when subjected to an electric field, thereby generating a pressure wave within the ink chamber and expelling an amount of ink through the chamber orifice. Both piezoelectric and bubble-jet methodologies are considered "drop-on-demand" or "impulse" technologies, i.e., a drop of ink is ejected from the print head only when desired.
Each type of ink jet print technology requires its own unique type of print head, and print heads may further vary based on parameters such as whether the print head contains only black ink, or whether it is capable of color printing. Generally, the different types of print heads are interchangeable, except that most printers are unable to accommodate both black ink and color due to physical differences between the print heads, i.e., print heads designed for color printing are typically larger to accommodate a variety of ink colors. Other print head parameters include architecture, resolution, number of ink jet nozzles, and spacing between the nozzles. Because print heads are interchangeable, the printer electronics must know what particular type of print head is installed, as well as information relating to the various print head parameters, so that algorithms within the printer control system can be reconfigured to provide appropriately formatted print commands to the print head electronics.
Therefore, it is desirable to provide the printer electronics with information relating to the characteristics of the particular print head that is installed. This can be done by digitally encoding the identifying information into the print head electronics and enabling the printer electronics to retrieve that information as it is needed.
A number of attempts have been made in the prior art to provide print head identifying information to the printer electronics. U.S. Pat. No. 4,872,027 to Buskirk et al. discloses providing extra electrical contact pads on the resistor network/array which fires the nozzles of the print head. These contact pads are selectively electrically connected in the resistor network to fire the individual nozzles in one of several unique configurations, each of which defines a specific print head. The code provided by these unique configurations of the electrical pads is detectable by the printer so that the type of head installed is determinable. This is accomplished by selectively connecting the individual electrical pads (or not connecting them) to the resistor circuits or circuit traces. By individually toggling the resistor lines at high or low voltage levels and detecting a voltage level shift on the lines associated with the extra contact pads, a connection (or lack thereof) may be detected.
Other prior art approaches to providing print head identifying information to the printer disclose identification circuitry disposed in the print head. U.S. Pat. No. 4,930,915 to Kikuchi et al. discloses print head identification means disposed in a print head. In one embodiment, a 24-pin print head is identified when the printer electronics read a "high" state value on a signal line interconnecting the printer electronics and identification means. A 9-pin print head is identified by a "low" state signal. In another embodiment of the Kikuchi invention, a parallel-serial converter produces a predetermined identification signal.
U.S. Pat. No. 5,363,134 to Barbehenn et al. discloses an integrated circuit for use in the print head of an ink jet printer. The integrated circuit includes an array circuit having a plurality of resistor cells arranged into rows and columns for heating an ink reservoir to produce a pattern of ink jets. A corresponding number of row and column lines are coupled to the array circuit for selecting and energizing the resistor cells according to the desired print pattern. An identification circuit is integrated into the same substrate as the array circuit. The identification circuit is programmable by means of a plurality of programmable paths corresponding and coupled to each row line. These programmable paths each include a programmable fuse and an active device connected in series. The opposite ends of the programmable paths are coupled together at a common node, which in turn is coupled to an output circuit for providing a single serial output signal in response to a sequential polling of the row lines.
The number of bits of identifying information that Barbehenn is capable of providing to the printer electronics is limited to the number of row lines available. For example, if there are a total of seven row lines interconnecting the array circuit with the printer electronics, then Barbehenn's identification circuit will be limited to storing seven and only seven bits of identifying information because each of the programmable paths correspond with and are coupled to a unique one of the row lines. To provide an identification circuit that contains greater than seven bits of identifying information, Barbehenn would be required to increase the number of row lines, or address lines available.
In addition to being limited by the number of available address lines, the amount of information that can be stored on a print head cartridge is also limited by cost and space considerations. Because most print head cartridges are disposable, it is very desirable to minimize their costs. Including large memory arrays on a print head chip increases the cost of fabricating the print head. Thus, while a large memory chip on the print head might be desirable from a memory standpoint, the additional cost of placing such a device on a disposable print head makes the solution economically undesirable. In addition, storing more information on the print head cartridge Increases the space requirement for the memory circuit on the print head. As the size of the print head substrate increases, the cost and complexity correspondingly increase.
Thus, there is a need for an efficient, inexpensive, print head identification circuit that uses a minimum number of components to store a maximum amount of information and preferably is not limited by the number of address lines interconnecting the existing print head electronics and printer electronics.